More-Precise Genetic Engineering for Plants

New technology makes it possible to alter plant genes precisely and efficiently.

Genetically engineering plants is a time-intensive process. Methods currently used to deliver genetic changes are imprecise, so it's often necessary to generate thousands of plants to find one that happens to have the desired alteration. Two papers in this week's Nature detail the use of a genetic technology that allows scientists to target plant genomes more precisely. The method, which has previously been used in animals and in human cells, can be used to introduce a new gene, make small changes in existing genes, or block a gene from being expressed; it also makes it possible to introduce several different genetic changes into the same plant.

Gene fixing: Using a new technique, researchers altered a gene in tobacco plants to make them herbicide resistant. The plants shown on the left are able to thrive when exposed to herbicide, compared with control plants at right. Credit: Daniel Voytas

"We now have some control over the plant's genetic code," says Daniel Voytas, lead author of one of the papers and a geneticist at the University of Minnesota. The technique not only allows for more precise changes, but it greatly increases the efficiency of generating genetically engineered plants for use as food or fuel, or for absorbing carbon and cleaning the environment. "If you can deliver a gene to the same location every time with precision, that might change the regulatory landscape and decrease the cost of creating these transgenic plants," he says.

Vipula Shukla, a scientist at Dow AgroSciences, who led the other study, says that for plant scientists, "all of the conventional tools that are available to us are based on methods that make random modifications to plant genomes." These methods include using a bacterial vector to transfer DNA into a plant cell, or physically blasting DNA-coated particles into cells. DNA introduced these ways, Shukla says, can land anywhere within the plant's genome and have unintended side effects like altering an existing gene or producing multiple copies of the gene of interest. Scientists typically generate many plants and then screen them to find the ones in which the desired change was successful.

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Both of the new studies--one was led by Dow and another by an academic consortium--employed a gene-targeting technology called zinc finger nucleases--synthetic proteins that can precisely target locations in the genome and make specific genetic changes.

Zinc finger nucleases work by breaking both strands of DNA at a specific site in the genome. This double break prompts the cell's own repair machinery to patch the rift. The machinery will often search for a piece of DNA that is similar to the damaged region to copy and paste back into the genome. By supplying a piece of DNA that contains sequences from the original gene with the desired changes--either the addition of a new gene or a change in sequence--scientists can induce the cell to change the genetic code as it repairs the break. The technology can also be used to block a gene by taking advantage of another repair mechanism in which the cell simply joins the two broken ends back together, which often deletes or inserts new DNA sequences into the repair site, resulting in DNA code that can't be read properly.